With very short wavelength and strong penetration capacity, an X ray can achieve a penetration rate of 100% at an atmospheric pressure of less than 10−4 Pa when the photon energy of the X ray is more than 10 keV (namely, the wavelength of that is less than 0.12 nm), which is nearly unattenuated transmission. That is to say, a long-distance space communication can be implemented by a very small transmission power. In another scenario, a satellite needs to pass through a plasma zone in which the radio wave is completely shielded when returning to the earth, but in the plasma zone, and then the satellite can pass through the plasma zone by the X-ray communication. Therefore, compared with other communication ways, the X-ray communication has the advantages of low transmission power, long transmission distance, high confidentiality, freedom from electromagnetic interference in space environment and wide communication band, by which the real-time communication among space satellites in the future can be expected to be realized.
Dr. Keith Gendreau from Goddard Center Flight Center of America had proposed that a point-to-point communication among space satellite aircrafts could be realized by an X ray in 2007, and he also built an experimental facility of this proposal. As shown in FIG. 1, an Ultraviolet Light-Emitting Diode (UV-LED) is modulated at a transmitting end by a digital signal, and then the modulated ultraviolet light which is emitted by the UV-LED irradiates a “photoelectric emission X-ray tube”, wherein the “photoelectric emission X-ray tube” consists of an ultraviolet photoelectric cathode, a Micro-channel Plate (MCP) and a metallic target anode. The photoelectric cathode receives ultraviolet light and converts it into photoelectrons, and the photoelectrons are multiplied by the MCP, and then are accelerated in anodic electric field (Va) to bombard a metallic target, so as to generate a modulated X-ray pulse. In a receiving end, the modulated X-ray pulse is converts into a modulated electric pulse by a Si-PIN photodiode sensitive to the X ray, and then the modulated electric pulse is filtered and is processed by a demodulation circuit to be reverted into a digital signal.
To sum up, obviously, the scheme of Dr. Keith Gendreau mainly has the following defects:
1) The signal-to-noise ratio of communication is low and the error rate of communication is high: The photoelectric emission current of the photoelectric cathode is direct ratio to the power of incident light, but the photoelectric cathode will be subject to damage in perpetuity if the power of the incident light increases to a certain value, so that the current (Ia) cannot be too large. Therefore, in the scheme of Dr. Keith Gendreau, the transmission power (Ia*Va) of the modulated X-ray pulse source cannot be very large, accordingly, the communication signal-to-noise ratio is low and the error rate is high.
2) the speed of communication is low: In the scheme of Dr. Keith Gendreau, since both of scattering and focusing for the X ray are all difficult to be realized, a large-area Si-PIN photoelectric diode is adopted to detect an X-ray pulse in order to implement long-distance communication. The large-area Si-PIN photoelectric diode utilizes internal photoelectric effect, and the time resolution is only the magnitude of millisecond, so the communication speed is limited. The disclosure is to provide a space X-ray communication scheme in order to overcome the defects above.